During the campaign, Donald Trump endorsed medical marijuana and said pot legalization “should be a state issue, state-by-state.” Attorney General Jeff Sessions, on the other hand, is a fierce opponent of marijuana and has opposed measures that would limit the federal government’s ability to interfere with state decriminalization efforts. Last month, Sessions reiterated the federal government’s authority to enforce federal drug laws “regardless of state law,” and some fear he will resist congressional efforts to protect medical marijuana from federal drug laws. Yet Sessions is not the greatest threat to continuing state-level marijuana reform efforts.

Lawmakers and citizen initiatives have successfully reformed marijuana laws in a majority of states. Twenty-nine states allow for the medical use of marijuana, according to the National Conference of State Legislatures. Eight have legalized marijuana possession and use altogether, allowing for recreational use. At least a dozen more states have effectively decriminalized possession of marijuana in small amounts. Yet marijuana use and possession remains illegal under federal law, even in small amounts or for medical purposes.

As a practical matter, the federal government has neither the interest in policing nor the ability to police low-level infractions of federal drug laws. Limits on federal law enforcement resources mean that the Drug Enforcement Administration focuses its efforts on larger dealing and trafficking operations. This policy approach was formalized during the Obama administration in the Cole Memorandum, which clarified that the Justice Department has little interest in going after marijuana possession or sale that is compliant with state law and is not linked to interstate trafficking or sales to minors. Nonetheless, the federal prohibition casts a shadow over marijuana-related businesses and activities that have been legalized under state law.

To protect state-level reforms, Congress has enacted appropriations riders that bar the DEA from spending funds to “interfere” with state laws authorizing the cultivation, use, possession or distribution of marijuana for medical purposes. Despite Sessions’s opposition, such a rider was included in the most recent spending bill that provides funding through Sept. 30.

The Appropriations Rider sends an important signal that Congress wants to allow states to allow medical marijuana, but it only goes so far. While the rider limits what the DEA can do, and was successfully invoked as a defense against prosecution in a case before the U.S. Court of Appeals for the 9th Circuit, marijuana use and possession remain illegal under federal law, and this has far-reaching implications. Marijuana reform advocates spend lots of time worrying that Sessions will find a way around the appropriations rider or depart from the set of priorities outlined in the Cole Memo. This threat is real, but other threats are greater.

The fact that marijuana possession remains illegal under federal law has far-reaching implications whether or not the DEA can raid medical marijuana dispensaries. For one thing, it means that banks cannot lawfully service marijuana businesses, as doing so means servicing a criminal enterprise. The result is that marijuana sales are conducted almost exclusively on a cash basis. (For more on the banking angle, see this excellent paper by Alabama law professor Julie Hill.) This cannot be fixed through an appropriations rider.

A bigger potential threat comes from the fact that marijuana possession and distribution are predicate offenses under the Racketeer Influenced and Corrupt Organizations Act (RICO). This means that those who produce or sell marijuana are potentially subject to civil RICO suits, whether or not such activities are legal under state law. So held the U.S. Court of Appeals for the 10th Circuit earlier this year. A federal judge once described RICO as “the monster that ate jurisprudence.” Barring real reform at the federal level, it could be the monster that ate marijuana federalism, too. Here again, an appropriations rider is insufficient.

The only way to protect state-level marijuana reform efforts is to change federal law, either by ending federal marijuana prohibition or expressly allowing state reforms to proceed. Outright federal legalization of marijuana is unlikely — and might not be a good idea insofar as state-level reform efforts generate useful information about the best way for reforms to occur. Allowing different states to adopt different policies encourages policy experimentation and produces knowledge about the pros and cons of different legal regimes.

The end of federal alcohol prohibition provides a potential model for how state-level marijuana reform efforts could be allowed to proceed. After adoption of the 21st Amendment, federal law continued to prohibit the sale and distribution of alcohol where such activities remained illegal under state law. Put another way, possessing, transporting and distributing alcohol in violation of state law was itself a federal offense. This remains true today. Thus, if a business produces alcohol in one state with the intention of exporting it to another state in violation of either state’s laws, it has committed a federal crime. In this way, the federal government allows each state to make its own choices with regard to alcohol policy and limits the effect one state’s choices can have on its neighbors. There’s no reason a similar approach would not work for marijuana.

Some opponents of state-level marijuana policy reform fear that legalizing marijuana in one state necessarily harms others. Such concerns are likely overstated, as Alabama argued in its powerful Gonzales v. Raich amicus brief, but can be addressed by limits on interstate trafficking, as has been done with alcohol. Marijuana would not be the first product to be legal in some states but not in others, and there’s no reason the traditional federalism principles are not equally applicable here. Perhaps Congress should give it a try.